1. Field of the Invention
The present invention elates to a throttle valve for an internal combustion engine provided with a conditioning circuit.
2. Description of the Related Art
A throttle valve, which is arranged upstream of an intake manifold and adjusts the flow rate of the air which is fed to the cylinders, is normally provided in internal combustion engines. Conventional throttle valves typically have a valve body provided with a tubular feeding duct through which the intake or compressed air for the internal combustion engine flows. A throttle plate is housed in the feeding duct and is splined to a rotating shaft to rotate between an opening position and a closing position of the feeding duct. The rotation of the throttle valve plate is controlled by an actuator device which typically includes an electric motor coupled to the throttle valve plate shaft via a gear drive and at least one spring which pushes the throttle valve plate shaft towards the closing position (or rather towards a limp-home position close to the closing position).
The electric motor has a cylindrical body which is arranged in a tubular housing of the valve body arranged by the side of the feeding duct. The gear drive is arranged in a chamber of the valve body, which is defined by two shells: a first shell defining a removable lid and a second shell arranged next to the feeding duct and next to the tubular housing.
The valve body further includes a conditioning circuit which is defined by a channel, which may assume various conformations and routes. Where the channel is substantially L-shaped, it has a major branch provided in the upper portion of the second shell and a minor branch provided in the upper portion of the tubular housing. The channel is in hydraulic communication with a pump, which circulates conditioning fluid and feeds the channel itself for conditioning the various parts of the throttle valve.
Published European Patent No. EP1348850 describes, for example, a throttle valve provided with a heating circuit adapted to prevent the freezing of the valve itself provided with an elastically deformable tube made of a fuel and oil resistant rubberized fabric arranged in a variable section channel of an appendix of the valve body having a smaller diameter than the diameter of the elastically deformable tube which is arranged inside it. Published German Patent No. DE19625154 instead describes a device for heating a throttle valve made with an appropriately shaped tube which is connected to the valve body via mechanical fixing, such as a pair of brackets for example. Further, a layer of heat-conducting paste is interposed between the tube of the heating device and the valve body. The heat-conducting paste does not have a structural function and therefore mechanical fixing is are needed to connect the tube to the valve body.
The entire valve body of most conventional throttle valves is made of metallic material, such as aluminum, and is monolithic (i.e. is formed seamlessly in one piece).
The valve body (i.e. the second shell, the feeding duct, and the tube housing) is made by casting (normally die-casting) and, if needed, is then mechanically machined. Pinholes and/or micro air bubbles may form in the valve body because the material is injected at relatively high temperatures (in the order of 700° C.), at equally high pressures (in the order of 1000 bar), and very rapidly for manufacturing the valve body by casting (normally die-casting). The pinholes and/or micro bubbles are difficult to see with unaided eye (but are visible only under X rays) and are difficult to identify during the step of setting and tuning the throttle valve.
Such pinholes and/or micro bubbles are particularly dangerous because with the aging of the valve body and, in the case of relatively high pressures involved, the passage of conditioning fluid in the conditioning circuit channel may put different micro bubbles into mutual communication and thereby cause the formation of channels for the passage of conditioning fluid towards the other components, in particular towards the electric motor, towards the feeding duct, or towards the outside environment.